Just to ruin it for everyone... :)
I read somewhere that it's water droplets on the lens of the camera, which is why they're all in a line - it's the same drop taken at different times as the plane (presumably) flew across the landscape.
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That wouldnt explain why when you zoom out they get smaller... I'm thinking its a fleck of dust on the image itself.
I, for one, welcome our new quasi-sperical overlords.
Here's the discussion from Google Sightseeing: http://www.googlesightseeing.com/2005/05/12/ufo/